1. Technical Field
The invention is in the field of heat transfer devices, and methods for operating such devices. In particular, the invention relates to devices that transfer heat by moving fluid through a closed loop.
2. Description of the Related Art
Prior art closed loop thermal transport systems may generally be divided into two types, active circulation systems and passive circulation systems. Active circulation systems, such as mechanically-pumped loops, involve forcing flow through a loop containing an evaporator and a condenser, for example, utilizing any of a wide variety of mechanical pumps. Passive systems include devices such as heat pipes and capillary-pumped loops, which transport heat by evaporating and condensing the fluid, and transport the fluid through use of capillary forces.
Actively-pumped thermal loops can have the disadvantage of the weight, size, cost, and mechanical complexity that occur is systems with a pump. Passive systems avoid the disadvantages of utilizing a pump. However, passive systems exploiting capillarity may suffer from limited fluid flow and/or heat transfer capability that regulates them to situations where only small thermal and pumping loads are encountered.
It will be appreciated that there may be situations where the foregoing disadvantages of traditional systems are unacceptable. One example is for thermal systems on board satellites in which increased capabilities and decreasing size of satellites may push the requirements of on board thermal control systems beyond what can be obtained with traditional passive systems, and for which mechanically-pumped systems have unacceptable weight, size, and complexity. Another example is in cooling electronic systems, where small size and large heat removal capacity are highly desirable properties, without the added cost of a mechanical pump.
From the foregoing, it will be appreciated that a need exists for thermal systems which have greater capacity than traditional passive systems, yet avoid the size, weight, cost, and complexity of systems with mechanical pumps.
A pulse thermal loop heat transfer system includes a means to use pressure rises in a pair of evaporators to circulate a heat transfer fluid. The system includes one or more valves that iteratively, alternately couple the outlets the evaporators to the condenser. While flow proceeds from one of the evaporators to the condenser, heating creates a pressure rise in the other evaporator, which has its outlet blocked to prevent fluid from exiting the other evaporator. When the flow path is reconfigured to allow flow from the other evaporator to the condenser, the pressure in the other evaporator is used to circulate a pulse of fluid through the system. The reconfiguring of the flow path, by actuating or otherwise changing the configuration of the one or more valves, may be triggered when a predetermined pressure difference between the evaporators is reached, for example. A controller may be operatively coupled to the one or more valves to control the reconfiguration of the one or more valves. The controller may also be coupled to one or more transducers, for example include a differential pressure transducer, to gather information used in the controlling.
According to an aspect of the invention, a pulse thermal loop heat transfer system includes a pair of evaporators, each of the evaporators having an inlet and an outlet; a condenser operatively coupled to the inlet of each of the evaporators; and one or more valves between the outlets and the condenser. The one or more valves are operatively configured to selectively couple one or the other of the outlets to the condenser.
According to another aspect of the invention, a pulse thermal loop heat transfer system includes a pair of evaporators, each of the evaporators having an inlet and an outlet; a condenser operatively coupled to the inlet of each of the evaporators; and means for selectively operatively coupling each of the outlets of the evaporators to the condenser.
According to yet another aspect of the invention, a pulse method of transferring thermal energy with a heat transfer fluid in a closed system, the system including a condenser and first and second evaporators, includes iteratively switching between 1) putting the first evaporator into communication with the condenser to allow the heat transfer fluid to flow from the first evaporator to the condenser, while substantially blocking flow of the heat transfer fluid from the second evaporator to the condenser; and 2) putting the second evaporator into communication with the condenser to allow the heat transfer fluid to flow from the second evaporator to the condenser, while substantially blocking flow of the heat transfer fluid from the first evaporator to the condenser.
According to still another aspect of the invention, a pulse method of transferring thermal energy with a heat transfer fluid in a closed system, the system including a condenser and first and second evaporators, includes iteratively performing the steps of: configuring the system in a first configuration which allows flow of the fluid from the first evaporator to the condenser; waiting for a first triggering event; configuring the system in a second configuration which allows flow of the fluid from the second evaporator to the condenser; and waiting for a second triggering event.
To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
In the annexed drawings:
FIG. 1 is a schematic diagram of a pulsed thermal loop (PTL) in accordance with the present invention;
FIG. 1a is a side view of a passive flow selector which may be employed with a PTL in accordance with the present invention;
FIG. 2 is a high-level flow chart illustrating steps in the operation of the PTL of FIG. 1;
FIGS. 3-6 are schematic diagrams illustrating the configuration of the PTL during the steps of the method of FIG. 2;
FIG. 7 is a plot of pressure vs. time for the evaporators of the PTL of FIG. 1 during the steps of the method of FIG. 2;
FIG. 8 is a schematic diagram of an additional embodiment pulsed thermal loop (PTL) in accordance with the present invention;
FIG. 9 is a schematic diagram of another additional embodiment pulsed thermal loop (PTL) in accordance with the present invention; and
FIG. 10 is a schematic diagram of yet another additional embodiment pulsed thermal loop (PTL) in accordance with the present invention.